I am the original owner of a Conrad Johnson PV-12, which I purchased new from a dealer about 20 yrs ago. Up until around June of last year, it was all original, incl. the tubes. One day I discovered a high-pitched clanging noise when I tapped on the faceplate, and at the recommendation of Jeff Fischel from CJ, and several members from another forum, I got new tubes, direct from CJ.

That noise still exists, but I understand now, that it's due to the monophonics of the tubes. Which probably means I didn't really need to replace the tubes, but hey - they were 20 years old, so I am not going to complain.

The reason I seek help is not for that - it's for something else. I high-pitched noise that appears from time to time (without touching the unit), which I first noticed after the tube swap. This noise might have been present before the new tubes, and maybe I just didn't notice it. Regardless, I need help now. A little history:

After replacing the tubes, and then finding this noise soon after, I had brought the PV-12 to a local electronics dealer. He cleaned the switches, and contacts, and I was hoping that would be the end of it. I get the unit home, and it doesn't sound quite right. I call Jeff @ CJ, (who by the way was helpful and nice), and he says to me, "send me the unit and I will make it like new for you".

I send the unit to CJ, and get it back not too long a period of time later. Plug it in, and now it sounds as it should. Great. But the high-pitched noise is still there. It is highly possible that due to the complete randomness, Jeff (or whoever actually worked on the unit) did not come across the noise, and therefore a clean bill of health was in order at the time.

I then purchase another pair of op tubes - Mullard 12AU7s from another dealer - just to see if the unit acts the same way with diff tubes. Which it does, meaning the issue is something other than the tubes.

I then get back w/Jeff, who tells me I might have better luck with some EAST GERMAN 12AU7’s or PHILIPS 6189’s. I got a pair of the latter, but the ringing is still there.

The other thing that Jeff told me is that it is the tubes that is the issue (the tube grid oscillating), and not the unit itself.

I was wondering if anyone here has experience in this matter, and whether or not any of you have found a resolution.

I have had a PV12, but never this issue. I would get back with jeff F and relay to him what you have done as a troubleshooting method. I'd refer to send it back to them to have them replace the tubes and to test it. Question; were they ever able to recreate it in their labs when they had it? You did not say so. I love my old PV12 and no one has ever said a bad thing about them when working properly, so it is worth dealing with. If you are done and want to get away from it, let me know, otherwise I'd go back to Jeff F as I have said, and let them recreate the issue in the lab and let them replace the tubes after recreating the problem to ensure they are enjoined in the issue and the fix.